Question for those who use Ext/Off Camera Flash

[HPS3]

My setup is a Nikon D5100/SB 600. Last night I was using the flash to bounce off of a ceiling in TTL mode and the exposure was perfect(1/160, f2.8, ISO 500). When I tried to remove the flash and shoot with it off camera I found it was overexposing when I used the same camera settings. I was using the flash at 1/64th power which is the lowest it can go in Manual setting. Can the camera tell the flash to shoot at a lower power than 1/64th when it is mounted on the camera in TTL mode?

 

[wbeem]

My setup is a Nikon D5100/SB 600. Last night I was using the flash to bounce off of a ceiling in TTL mode and the exposure was perfect(1/160, f2.8, ISO 500). When I tried to remove the flash and shoot with it off camera I found it was overexposing when I used the same camera settings. I was using the flash at 1/64th power which is the lowest it can go in Manual setting. Can the camera tell the flash to shoot at a lower power than 1/64th when it is mounted on the camera in TTL mode?

TTL can vary the power in ways that Manual mode cannot. That's why you're experiencing different flash power. You can still use TTL with off-camera flash if you're using CLS to trigger the flash. You could also get the SC-28/SC-29 cord for off-camera flash without using CLS, if you don't mind being restricted by the length of the cable.

If you're unsure how to setup the SB-600 using TTL with CLS, let me know.

 

[HPS3]

Wbeem, I was hoping you would answer this question. As an admirer of your work, I notice that your lighting is always perfect. Is the CLS really important to use with off camera flash. I shoot with a D5100 without CLS. Right now I have some Promaster wireless triggers, 2 SB 600's, stands and shoot through umbrellas. Is it that hard to adjust flashes manually or should I look into purchasing SB700 or upgrading to the D7000 in the future(for the use of CLS). My friend wants me to take senior portraits of her daughter and I have a couple of months to practice with off camera flash. I have some ideas for natural light shots but also want to incorperate some flash shots.

 

[wbeem]

Thanks for the kind words.

CLS is just a built-in triggering system, but it does also allow the use of TTL. When you use radio triggers (with the exception of Radio Poppers), you can't use TTL. At any rate, now you understand why there's a difference in exposure between your on-camera (TTL) exposure and your off-camera (manual) exposure. TTL cheats by issuing controls to the flash that you can't duplicate manually.

So, here's what you need to keep in mind. In addition to the usual exposure triangle, adding flash gives you two more variables:

1: Flash Power
2: Flash to Subject Distance

You already reduced your flash power as much as possible. Your remaining choices are:

1: Change your Aperture to something smaller to reduce the amount of light hitting your subject. *

2: Move the flash further away from the subject. **
3: Use a Neutral Density (ND) filter to compensate for the power of the light.

Here's the caveats with my asterisks:

* If the background scene is important, changing the aperture will affect it because you've reduced the amount of ambient light entering the camera. You can reduce the shutter speed to compensate. The flash will keep your subject sharp (within reason, if we're not talking about very long exposures).

** The farther your Flash to Subject distance, the harsher the light becomes on your subject. If you want soft light, then you need a large light source relative to your subject. If this isn't a concern right now, then go ahead and move the light away.

If you're moving the light farther away from the subject, you need to keep in mind something called the Inverse Square Law. Basically, that law describes the decay of radiation, and light is nothing more than electromagnetic radiation that's within the visible spectrum.

Put more plainly, you lose TWO stops of light every time you double the distance from your Flash to Subject. If it's an inch away, you lose two stops by moving the light two inches back. Then another two stops at four inches, etc.

What happens is that you find there are zones of light that are very narrow up close, and the light falls off dramatically. As you get more distance, the zone of light within the same stop has more depth to it.

OK, does that help, or did I just throw too much babble at you?

 

[HPS3]

Hey Wbeem, thanks for all of the thorough info. I understand from what you said I could have reduced my ISO from 400 to 200 and lowered my shutter from 1/160 to 1/80 which would have kept my ambient the same but lowered my flash. Is this correct? Keeping the aperture the same.

 

[HPS3]

I had exposed this shot for the background but decided to darken the background in LR because is was too busy. This was just shot in my living room playing around with the SB600/33" ST umbrella.


_DSC3142 by Harry Shields, on Flickr

 

[wbeem]

Hey Wbeem, thanks for all of the thorough info. I understand from what you said I could have reduced my ISO from 400 to 200 and lowered my shutter from 1/160 to 1/80 which would have kept my ambient the same but lowered my flash. Is this correct? Keeping the aperture the same.

I'm glad you brought up the ISO, because I thought I forgot it with my previous post. I sort of assumed something, which isn't always a bright idea on my part.

Typically, you want to first get your ambient exposure. So, if you want it darker (like in your photo below), you underexpose the ambient light. When working with Manual Flash, I'd also suggest you work with Manual exposure controls. The reason for that is so you don't get a different exposure due to the meter reading changing from one pic to the next. When you keep everything manual, you keep everything consistent and easy to control.

I think your exposure on that portrait is great. In fact, I first thought you did it in camera by keeping the ambient light under-exposed. It looks like you have the hang of it. Now the thing to do is just play with it. Keep the same subject & background, and then adjust one setting up & down to see how it affects your image. Change the shutter speed up & down. Then change the Aperture up & down, etc.

Once you get comfortable with it, this stuff becomes second nature and you start reading the light with your eyes and get a pretty good feeling for a ballpark exposure.

 

[HPS3]

Thanks for all of your help.For this shot I used a 33" umbrella. if I shoot my neighbors portraits outside (half to full body), what size umbrella should I use?

 

[wbeem]

Thanks for all of your help.For this shot I used a 33" umbrella. if I shoot my neighbors portraits outside (half to full body), what size umbrella should I use?

How many neighbors at a time? Here's something to understand about light modifiers like umbrellas and soft boxes. If they get more than twice their diameter away from the subject, you lose any benefit of soft light. So put that 33" umbrella 66" away and you're still hitting them with hard light. The umbrella needs to be as close to them as you can get it to have the softest light.

Of course, light falls off faster at shorter distances, so that means you can have someone well exposed and the rest increasingly darker. Lighting a whole family at a time with one little umbrella is asking too much of it. You need to have more lights if you want to provide even, soft light on a family-sized group of people - or you need a much larger light modifier.

Photography is an exercise in compromise.

 

[HPS3]

The umbrella is for a senior portrait shoot with one girl. They are cheap enough I think I will pick up a 40" shootthrough.

 

[wbeem]

The umbrella is for a senior portrait shoot with one girl. They are cheap enough I think I will pick up a 40" shootthrough.

Oh, I think you'll be fine with the umbrella for just one subject. It never hurts to have a larger one. In fact, you can get one up to seven feet from Westcott for $99 and power it with your SB-600, no problem, if you go for group portraits.

The next thing I would recommend would be to get a reflector - preferably silver or possibly white, but not gold. The reason for the reflector is to provide some fill light.

As you start to get your light closer, that light falls off faster and leaves some shadows that may be undesirable. You want some shadows, of course, but how dark do you want those shadows? Having a reflector gives you a chance to bounce some light back where the main light isn't hitting.

Let me give you an example. Here are two shots out of camera where I was setting up my lighting. I'm using a 53" octa soft box behind her to make the white background. Above her, I have a 17" Beauty Dish. Notice how the light doesn't make it around her throat.

The next thing to do is bring in something underneath for a clamshell light, since this setup was for a beauty shot. You could put a silver reflector there to do the job. In this case, I put my SB-900 below in a 36" octa soft box for the fill light.

You can see that the fill isn't as bright as the key light on her face, nor should it be. However, I wanted to cut down that drastic change in lighting. The final shots, with retouching, looked like this one:


Sam MM #802603 by wbeem, on Flickr

Sometimes you WANT those shadows to be darker, but it creates a moodier scene, like this one:


No Drama, Please by wbeem, on Flickr

It's all about figuring out what you want to convey, and then using light falloff, fill, etc to sculpt the portrait.

 

[HPS3]

Thanks Wbeem for helping me understand light. Your portraits are awesome.